<!DOCTYPE html>
<style>
.item {
    margin-bottom: 5px;
}
.ref {
    width: 40px;
    height:40px;
    background-color: green;
    position: absolute;
    top: 10px;
}
.test {
    width: 40px;
    height:40px;
    background-color: red;
}
.container {
    position: relative;
    margin: 0px;
    padding: 0px;
}
</style>
https://code.google.com/p/chromium/issues/detail?id=321295
The top and bottom margins of a box collapse together only if they are the  "top and bottom margins of a box that does not establish a new block formatting context".
<br>
There should be no red below.
<div class="container">
    <div class="ref"></div>
    <div>
        <div class="item" style="-webkit-columns: 10px 2;"></div>
        <div class="item" style="-webkit-columns: 10px 2;"></div>
        <div class="test"></div>
    </div>
</div>
